Master cylinder for hydraulic brake systems



Nov. 22, 1938.

J. w. WHITE 2,137,554

MASTER CYLINDER FOR HYDRAULlC BRAKE SYSTEMS Original Filed Nov. 8, 1928 Mid/4f Wag-52 ATTORNEYS Patented Nov. 22, 1938 UNITED STATES MASTER CYLINDER FOB HYDRAULIC BRAKE SYSTEMS John W. White, Detroit, Mich., assignor, by

mesne assignments, to Bendix Products Corporation, a corporation of Indiana Original application November 8, 1928, Serial No.

317,933, now Patent No. 2,030,340, dated February '11, 1936. Divided and this application August 24; 1931, Serial No. 559,109

v 9 Claims.

The invention relates to hydraulic vehicle brake systems and forms a division of my co-pending application for patent Serial No. 317,933, filed November 8, 1928 which has now issued as Patent 5 No. 2,030,340. The subject matter of the present application is the master cylinder through which fluid pressure is supplied to the brake cylinder and the invention consists in the construction as hereinafter set forth.

In the drawing:

Figure 1 is a diagrammatic view illustrating a system embodying this invention;

Figure 2 is a sectional view on a large scale of the master cylinder by which pressure is applied 15 upon the fluid in the system;

Figure 3 is an end elevation of such cylinder, certain parts being broken away.

Figure 4 is a detail of the breather valve.

The braking system which embodies one appli- 20 cation of this invention is illustrated in Figure l as comprising a master cylinder A by which pressure is applied to the fluid, a plurality of brake cylinders B by which the pressure on the fluid is transmitted to the wheels, and conduits C connecting the master cylinder with the brake cylinders. Pressure is created in the master cylinder A by any suitable means as by a brake pedal D and the operation of the master cylinder actuates a stop light E.

The master cylinder A is separately illustrated in Figs. 2 and 3 and as there shown comprises a casing I suitably mounted upon a cross channel member 2 of a motor vehicle, being secured thereto by bolts 3. Within the casing I is a 35 pumping chamber 4 and a reserve or supply chamber 5 which chambers are connected by a port 6. At the forward or inner end of the chamber are outlets i, 0, the outlet i leading to the conduit C and thence to the brake cylin- 40 ders B and the outlet 8 receiving a stop light switch 9 by which the stop light E is controlled. The switch 9 is substantially that set forth in my'copending application Serial No. 241,805, flied December 22, 1927 which has now issued as 45 Patent No. 1,840,340, and hence need not here be described in detail.

Within the chamber 4 is mounted a piston l0 actuated by the brake lever D, which piston normally rests against a ring H at the mouth of the g chamber, being held in such normal position by a spring i2 attached to the tip of the lever D and to the channel member. The piston i 0 is carried by a rod l3 which passes through an opening in the cross channel member 2. The 55 rod l3 may be actuated in any suitable manner to advance the piston into the chambend and is here shown pivotally secured at its outer end to the brake lever D. The inner end of the rod I3 is preferably ball shaped and enters a semispherical depression It in the outer end of the piston l0, being held therein by a pin l5 which locks the rod to the piston while permitting pivotal movement in the depression around the pin as the rod I3 is actuated by the lever D. Mounted on the inner end of the piston I0 is a flexible cup l6 (preferably of rubber) secured in place by a screw l1 and washer H0.

The chambers 4 and 5 are connected not only by the port 6 but also by a passage ID, the outer end of the piston l0 being cut away at 20 so that the passage i9 is open regardless of the position of the piston i0. Surrounding the inner end of the rod I3 is a boot 2! preferably conical and of flexible material. The inner and larger end of the boot 2i is clamped between the casing l and the cross member 2 by the bolts 3, an annular recess 22 being formed in the outer wall of the casing to receive the edge of the boot. The outer and small end of the boot is inverted as shown in Fig. 2 and wired or otherwise rigidly secured in a recess 23 on the rod B3. The ends of the boot are thus sealed and the interior of the boot is in direct communication not only with the chamber provided in the casing i and is sealed by a needle valve 25. Threaded into the storage chamber 5 is a breather cap 26 having a passage 21 therethrough. The upper end of the passage 21 is open at all times to the atmosphere but across the lower end of the passage 21 is a disk 20 of rubber or other flexible material, secured at its periphery to the cap 26 and provided with inter secting slots 22 (Fig. 4). The disk 28 normally closes the passage 21 but any vacuum in the chamber 5 will be broken or any excess in air pressure therein will be relieved by a flexing of the disk and a consequent opening of the slots. One or more longitudinally extending grooves or passageways in the piston I 0 allow liquid to enter the cylinder chamber 4 past the cup it when a vacuum is set up in the chamber. This is one 0! the important features of the invention, as will be explained later.

As the present invention relates solely to the master cylinder it will not be necessary to describe the hydraulic brake system in further detail. In general, however, the system may be filled through the orifice 24 leading into the chamber 4 and through the port 6 into the chamber 5, through the passage l9 into the boot 2| and through the conduit G into the brake cylinders B which are provided with suitable venting means (not shown) for permitting the escape oi air. The air trapped in the chambers 4 and 5 is permitted to escape through the breather cap 28 previously described. However, the port 6 between the chambers 4 and 5 is so constricted that the chamber 5 will not be filled completely until after the conduit 0 and brake cylinders B are filled. When the system is filled the orifice 24 is closed by the valve and upon each forward stroke of the piston l0 past the port 6 fluid is forced from the chamber 4 of the master cylinder through the conduit C into the brake cylinders B which are actuated to apply the brakes. Upon the release of the brake lever D the spring [2 draws the piston I 0 .back, moving it faster than the fluid is returned from the conduit C into the chamber 4, thus creating avacuum which is filled from the storage chamber 5 by the flow of fluid through the grooves 30 and past the cup l6. This over-fills the system and when the fluid is forced into the chamber 4 by the return of the brake cylinders to normal position, the excess fluid will pass through the port 6 into the storage chamber 5.

While the breather cap 26 is provided, there will be practically no breathing action in the storage chamber because the boot 2| telescopes on itself and the fluid therein will pass forward with the piston and is of the same displacement. The boot ,ZI thus functions not only to seal the system and permit the operation of the piston ill, but also as a container for fluid supplementing the function of the storage chamber 5.

The system is thus kept at all times completely filled with fluid and the brake cylinders are hermetically sealed. Any variance in the volume of the fluid due to expansion or contraction under weather conditions will be compensated for by the master cylinder without any attention on the part of the operator. Furthermore, any vacuum formed due to the retraction of the piston Ill will cause no disturbance in the operation 'of the device because the wheel cylinders Bare hermetically sealed, but will draw additional fluid temporarily into the system. No air can enter the system so long as there is any fluid in the storage chamber 5 and thus theoperation of the brake will remain uniform.

What I claim as my invention'is:

1. In a fluid braking system, a master cylinder including a pumping chamber, a piston in said chamber, a supply chamber formed with a wall, means actuating said piston and extending from one end of said pumping chamber, and a hood attached to said actuating means and to said wall, said supply chamber communicating with said hood and sealing said piston at the outer end of said pumping chamber.

2. In a fluid braking system, a master cylinder including a pumping chamber and a supply chamber in communication with one end of said a pumping chamber, a piston in said pumping ume in said supply chamber during displacement.

of said piston.

3. In a fluid braking system, a master cylinder including a cylindrical pumping chamber and a supply chamber communicating with one end ofsaid pumping chamber, a piston in said pumping chamber, a piston rod for actuating said piston, a flexible hood surrounding said piston rod and connected thereto at one end, the opposite end being connected to said master cylinder to place the space within said hood in communication with said supply chamber, said hood being fashioned to telescope with itself during inward movement of said piston rod and to maintain substantially constant volume in said supinder,'a piston in said cylinder, a supply chamber having a wall and communicating with said cylinder at one end and sealing said piston, a rod for actuating said piston, a hood surrounding and connected to said rod and to said wall adapted to maintain a substantially constant volume in said supply chamber during displacement of said piston and a breather for said supply chamber normally sealing the same from the external atmosphere but permitting slight ingress or.

egress of air to compensate for any change in fluid volume in the said chamber.

6. In a hydraulic brake system, a master cylinder, a piston movable therein, a flexible boot enclosing the rear side of the piston forming a fluid chamber, a fluid reservoir, means for providing communication between said chamber and the reservoir, means for providing communication between said chamber and the cylinder during retractile movement of the piston allowing fluid from the chamber to enter the cylinder, said cylinder having an 7 aperture immediately in front of the retracted position of the piston whereby excess fluid in the cylinder may be returned to the reservoir.

'7. In apparatus of the class described, a liquid pressure cylinder and piston therein, a piston actuating element, means forming a liquid chamber at the rear of the piston, said means comprising extensible liquid retaining means surrounding the actuating element, a reservoir for the operating liquid communicating with said chamber, and means including an aperture in the wall of the cylinder to provide fluid communication between the reservoir and the pressure developing end of the cylinder when the piston is in retracted position.

8. In a hydraulic brake system, a master cylinder, a piston movable therein, a fluid reservoir communicating with the pressure developing end of the cylinder when the piston is in retracted position, a flexible boot enclosing the end of the cylinder rearwardly of the piston, and means for providing fluid communication between the reservoir and the boot. I

9. In a hydraulic brake system, a master cylinder, a piston movable therein, a fluid reservoir, said cylinder having a plurality of apertures communicating with the reservoir, one of said apertures being located immediately in front of the retracted position of the piston, and the other aperture leading to the rearward side of the.piston, and a flexible boot forming a variable volume means enclosing the rearward side of the piston and adapted to receive fluid from said reservoir through the aperture at the rearward side of the piston to seal the piston against the atmosphere.

JOHN W. WHITE. 

